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getting there with my mig machine

I had asked around over the last few years about a mig or a tig for my boat projects. i finally bought a miller 250 mig machine with a 30A spool gun..

I warped the heck out of my transom while filling the I/O hole ...luckily i am straightening that out slowly..

Today i ran home from work at 3:30 and started cutting my 1.5 x1.5" aluminum for my outboard bracket. I set up everything on a 3/4" piece of plywood outside( no work shop big enough) I have it figured out mostly on a cad program...so i had the "sizes" written down..and i had made up a woeden mock up first. I went to town by 9:30 pm I had this done:

the 80/20 stuff i got from work...was obviously clear anodized.. and gave me a little trouble...plus it has thin and thick portions... but I used it because that will be bolted to the boat and I wanted a beefier frame than the 1.5" square tube with .125" wall. the rest is the tube i bought. the square tube welded real nice.... I played with the feed and finally dialed in a good weld....I got it all together, and i clean up all the welds and go over it again for stronger welds. the middle frame, I will add .250 plate to to stiffen the sides and the top, because that is where the motor will hang Ill have a 3/4" plate for the motor mount side....the rest will just get covered with 1/8 sheet.....i really love Mig welding.... I just think I will be able to use this machine a lot more than i was led to beleive over the years... the boat work doesnt have to be pretty and there is usually so much of it, Tigging it would take hours

Is this a Starcraft Cheiftain you are working on? What size outboard are you mounting to it?
I would consider running another brace from the top tube that bolts to the transom, diagonally to the 2 horizontal pieces on either side of where the motor is going to mount, right where they meet the rear tube. This would help spread out the load across the back of the boat more when you hit the throttle. It will have a tendancy to torque up, pushing forward against the boat on take off. That is, the prop trying to go under the stern. That will put most all the stress dead center of the stern without those two other pieces running out to the corners of the boat.

Comment

that bracket frame isn't finished.... that was just what I did last night!.. I will weld 1/4" plate on the top middle section as well as the sides... as we'll as add those last two braces plus their verticle counterparts... then the aluminum sheeting will be welded...it will be plenty strong.. Ill have a aluminum U channel on the inside the full width of the transom under the bolts across the top of this bracket...and ill have braces going down to the last three ribs from that U channel!!

bob

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Is this a Starcraft Cheiftain you are working on? What size outboard are you mounting to it?
I would consider running another brace from the top tube that bolts to the transom, diagonally to the 2 horizontal pieces on either side of where the motor is going to mount, right where they meet the rear tube. This would help spread out the load across the back of the boat more when you hit the throttle. It will have a tendancy to torque up, pushing forward against the boat on take off. That is, the prop trying to go under the stern. That will put most all the stress dead center of the stern without those two other pieces running out to the corners of the boat.

I did look at it and was going to weld a sheet on each side of that inner frame, but decided to weld two braces similar to what you suggested, but anchored at the top of the back side to keep the motor from trying to pry the top back frame off the unit...

the braces arent welded yet... I will add a 1/4" plate on the TOP of the middle frame... that and all the 1/8th" sheet all around should make this bracket plenty strong... I have a 3/4" thick plate for the motor mount ...

bob

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I would think, put the 1/4" plate on the OUTER top frame(either side of O/B) to distribute the load to the top frame at the stern, leaving the area directly in front of the O/B open. If you box in the 2 side cavities, you can fill them with foam flotation to keep the O/B above water should the boat fill up. 1/8" plate will do fine for this area, and extra strength and rigidity.